Quick insert change system for multi-material plastic injection molds

ABSTRACT

An injection mold is provided which has a cavity plate, and a core plate. There are one or more insert slots in the cavity plate and the core plate. Each insert slot is capable of receiving an insert. The cavity plate and the core plate also have guide elements thereon, which guide elements are constructed and arranged so that, in use, an insert may be engaged with the guide elements and moved along the guide elements to the insert slot.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is the 35 U.S.C. 371 national stage of International ApplicationPCT/NZ02/00032 filed on 14 Mar. 2002, which designated the United Statesof America.

TECHNICAL FIELD OF THE INVENTION

This invention relates to an injection mold and has been designed inparticular to allow injection molding of plastic products utilising twomaterials.

BACKGROUND ART

Two material injection molding may comprise the injection molding ofplastics materials having different characteristics so as to provide acomposite product. Two material injection molding may, for example,allow an elastic plastic material to be molded onto a rigid plasticmaterial to improve the feel or touch of the material, allow forabsorption of shock and vibration and/or to provide sealing againstdust, water and other agents. Other applications of two materialinjection molding technology includes plastic parts with moveableassemblies, living hinges, decorative features, combinations oftransparent and non-transparent areas, different colours and the like.

In two material plastic injection molding technology currentlyavailable, commercially available injection molding machines areprovided with a mold specifically built for the product. These moldscommonly have two internal passages directing the two plastics materialsinjected by the molding machine to the two mold stations which have beenconstructed to correspond, or be complementary, to the geometry of theplastic part. Each of the two mold stations is made up of a group ofinserts constructed of tool steel to the required geometry. Productionof the plastic part involves injecting the first material into the firststation and then transferring the partially completed plastic part tothe second station where the second material is injected. With suchconventional two material injection molding technology, change over ofproduction from one product to another requires replacement of theentire mold and subsequent readjustment of the injection moldingmachine. Such a process typically takes about four to six hours tocomplete.

Thus conventional two material injection molding involves two majorequipment items. Firstly an injection molding machine with the abilityto inject two plastic materials sequentially into a mold, and secondlyan injection mold comprising a mold framework and a non-changeableplastic insert made according to the geometry of the two materialplastic product. The mold framework, which is commonly known as the moldbase, used in such conventional two material injection molding, isessentially the same as those designed for a single material injectionmolding. The mold base may be mounted on a turntable device built as anintegral part of the molding machine. Rotation of the turning deviceenables two different materials to be injected sequentially into theproduct inserts thus forming a two material plastic part. Rotation ofthe turntable thus is about an axis which is transverse to the axis ofmovement of the moving part of the mold framework.

The principal disadvantage of such constructions is the significanttime, as stated above, which it takes to change the two materialinjection molding device from a first set up to mold a first product toa second set up to mold a second product.

OBJECT

It is therefore an object of the present invention to provide aninjection mold which will obviate or minimise the foregoingdisadvantages in a simple yet effective manner or which at least providethe public with a useful choice.

DISCLOSURE OF INVENTION

Accordingly in one aspect the invention consists in an injection moldincluding a cavity plate, and a core plate, one or more insert slots inthe cavity plate and the core plate, each insert slot being capable ofreceiving an insert, the cavity plate and the core plate having guidemeans thereon, the guide means being constructed and arranged so that,in use, an insert may be engaged with the guide means and moved alongthe guide means to the insert slot.

Preferably the guide means comprise a channel or channels, or rib orribs.

Preferably both the cavity plate and the core plate have guide meansthereon, both the cavity plate and the core plate being able to receiveat least two inserts.

Preferably each guide means comprises a pair of spaced apart mutuallyinwardly facing channels or channel segments extending in a directionparallel to a line transverse to an axis formed by the movement of moldparts to open and close the mold in use.

Preferably the cavity plate and the core plate each include a removablemember which when engaged with the remainder of the cavity plate or coreplate closes the channels to substantially prevent movement of an insertinto or out of the insert slots.

Preferably one cavity plate is fixed and the core plate is moveablealong the axis.

In a further aspect the invention consists in an injection mold asdescribed and a plurality of inserts, the inserts having complementaryguiding means thereon to enable the selected insert to be entered intoand subsequently removed from an insert slot by engagement of the guidemeans with the complementary guiding means.

Preferably the complementary guide means comprises a pair of ribs ableto engage a channel in the cavity plate.

Preferably the core plate has at least two insert slots and is rotatableabout the axis to present a selected core insert to each cavity insertin the fixed cavity plate.

Preferably the core plate and the cavity plate each have the same numberof insert slots.

Preferably the core plate is mounted on an axle positioned along theaxis and drive means are provided to rotate the axle and thereby torotate the core plate.

Preferably the drive means comprise a pinion on said axle and at leastone moveable rack engaged with said pinion.

Preferably a pair of parallel racks are provided, the pinion beingpositioned between and engaging each rack.

Preferably the racks are moved by a piston and cylinder assembly.

Preferably each rack is moved by a piston and cylinder assembly arrangedto rotate the pinion in an opposite direction.

To those skilled in the art to which the invention relates, many changesin construction and widely differing embodiments and applications of theinvention will suggest themselves without departing from the scope ofthe invention as defined in the appended claims. The disclosures and thedescription herein are purely illustrative and are not intended to be inany sense limiting.

BRIEF DESCRIPTION OF DRAWINGS

One preferred form of the invention will now be described with referenceto the accompanying drawings in which,

FIG. 1 is a side elevation of a mold according to the inventionincluding injection molds according to the invention,

FIG. 2 is a perspective view of the injection mold of FIG. 1, showing inparticular a two colour mold,

FIG. 3 is an exploded view of a hydraulic system module for use in theinjection molding device of FIGS. 1 and 2 to drive and rotate a rotarycore plate included in the invention,

FIG. 4 is an exploded view of a rotary core module for use in theinjection molding device of FIGS. 1 and 2,

FIG. 5 and FIG. 6 are perspective views of the construction of FIG. 4showing inserts respectively in place and removed from insert slots in arotary core plate,

FIG. 7 is an exploded view of a fixed cavity module for use in theinjection molding device of FIGS. 1 and 2,

FIGS. 8 and 9 are perspective views of the fixed cavity module showingcavity inserts respectively in position and removed,

FIG. 10 is an exploded perspective view of a manifold plate modulehousing a hot runner manifold system.

BEST MODE FOR CARRYING OUT THE INVENTION

Referring now to the drawings, FIG. 1 shows an injection molding device.The construction can be for a two-colour product, or other two materialproducts. The region marked “A” shows a manifold plate module, theregion “B” shows a fixed cavity plate module, the region “C” shows arotary core plate module including a rotary core plate and the region“D” shows the hydraulic system.

The region “D” provides rotation of the rotary core plate module “C” andthe ejection mechanism for the molded articles. The device is driven bya molding machine (not shown) in use.

The hydraulic system “D” comprises a pair of plates 10 and 11 which areheld together by suitable bolts and threaded receiving depressions.

Apertures such as 12 are provided, for example, at or adjacent thecorners of the plates 10 and 11 and suitable centering sleeves areprovided. A pair of substantially parallel depressions 14 and 15 areprovided in the plate 10 along with a central aperture 16. The plate 11has a corresponding central aperture 17.

The central aperture 16 intersects the channels 14 and 15. Into theaperture 16 is provided a pinion 20 and this is driven by one or more,preferably a pair of racks 21 and 22 which engage each side of thepinion 20. The racks 21 and 22 are each moved by a piston such as piston25 operating in a cylinder 26 and 27, but in opposite directions, thustogether the racks 21 and 22, in one step of the molding cycle rotatethe pinion in one direction and in another step of the molding cycle theracks 21 and 22 rotate the pinion in the other direction. Bearings 28and 29 are positioned in the apertures 16 and 17. The pinion 20 has acentral bore 23 or non-round such as square cross section.

The ejection system comprises an axle in the form of a piston 30 and acylinder 31. Towards the other end of the cylinder is provided an armmounting sensor pin 32 which is able to become positioned adjacent aproximity switch 33. The construction is mounted on a mounting plate 34.Also mounted about the axle 30 is the cylinder cover 35. The signal fromthe proximity switch is integrated with the molding machine so that theejector system extends to eject a completed part.

The rotary core plate module at “C” comprises a plate 40 which isengaged with the plate 11. Attached to the plate 40 is a rotatable plate41 which has a non round, that is to say, preferably rectangular centralaperture 42. A shaft 43 is provided with a rectangular end part 44 whichis positioned within the rectangular aperture 42. The shaft 43 engagesthe rectangular bore 23 of the pinion 20. The pistons of the piston andcylinder assemblies 26 and 27 move the pinion 20 which in turn rotatesthe shaft 43 and in turn rotates the rotatable plate 41.

Thus when the pistons and cylinder assemblies 26 and 27 are operated theeffect is to rotate the plate 41.

The plate 41 provides the base of a rotating core plate. The rotatingcavity plate may be completed as follows. In the following example, theplate has two insert slots into which inserts can be placed.

The insert slots are provided by a central cross member 55 spaced apartfrom two end members 56 and 57. End members 58 and 59 complete theinsert slot. The end members 58 and 59, or at least one of them, arereadily removable, for example, by undoing fixing bolts. Guide means areprovided and these, in the preferred form, comprise channels or ribs. Inthe constructions shown, channels are provided. Thus referring to alower cavity, channels 61 and 62 are provided along the upper and lowerfaces. These channels are parallel to a line transverse to an axisformed by shaft 43. Into the upper insert slot similar channels areformed.

The end members 58 and 59, if desired, may be formed in two pieces ascan be clearly seen in FIGS. 5 and 6.

The core inserts each comprise a shaped member. Core insert 70 in FIG. 6carries cooperating guide means formed in this case by ribs 71 and 72.The other core insert 73 is similarly formed.

The fixed cavity plate is formed by a base plate 80 onto which a centraldivider 81 is provided upper and lower cross members 82 and 83 with sidemembers 84 and 85 to form a lower insert slot 86 and an upper insertslot 87 substantially as described for the rotational cavity plate.Cavity inserts 90 and 91 are provided in substantially the same manner,for example, the insert 91 having an upper rib 92 and a lower rib 93slidable in channels 94 and 95. As can be seen from FIG. 9 the channel95 is in effect provided in segments as are the central channels shownin FIG. 6. Again the cavity inserts 90 and 91 can be readily removed andinserted by the removal of one or both of the end posts 84 and 85.

Referring now to FIG. 10, the manifold plate is shown. This comprises apair of plates 100 and 101 backed by a thermally insulating plate 102. Aplastic injection module or manifold block 105 is provided to feed hotnozzles such as 106 and 107.

The hot runner assembly is substantially standard except for thepositioning of the hot runners 106 and 107. One material is injectedthrough insertion point 112 through position 111 and the other throughinsertion point 110.

Thus, in use, core inserts 70, 73, and cavity inserts 90 and 91 areselected and positioned in the insert slots as above described. Thepairs of inserts 70 and 91 and 73 and 90 are arranged so that one pairhas more tool metal removed to accept the second material. The moldingcycle begins with the injection molding machine in a fully closedposition and the first plastics material is injected into one pair ofinserts, for example, inserts 73 and 90 through injection point 112,while the second pair of inserts remains unfilled.

The injection molding machine then extends the mold parts “C” and “D”and the pistons and cylinders 26 and 27 are operated as required to movethe racks 21 and 22 and in turn the pinion 20 so that the moveable coreplate rotates through 180° (in the construction described) and themolding machine moves parts “C” and “D” to close the mold. Secondplastics material is then inserted into the pair of inserts 70 and 90,while a first injection of the first material can now be placed into theinserts 73 and 93. The molds are then again opened by the moldingmachine, the completed plastics item is then removed from insert 70 bythe ejection system driven by cylinder 3, and the piston and cylinders26 and 27 again operated to again rotate the mold through 180° when itis reclosed and an injection of the second material is injected into thepair of inserts 73 and 90 and simultaneously a second injection of thefirst material is injected into the pair of inserts 70 and 93. Theprocess can then continue.

Thus it can be seen that an injection molding device is provided whichhas some advantages. In the preferred form a simple mechanism isprovided to move the rotary mold between the two required moldingstations. It is a particular advantage of the preferred form of theinvention that in order to change to mold a second, third or forthdifferent product requires only the removal of a small number of boltedon parts which close the channels into which the inserts run, to allowthe inserts to be then removed, replaced and the stock rebolted backinto place, this is advantageous. Thus the need to replace the entiremold when changing products is substantially eliminated. This achieves asignificant saving in tooling cost. In particular the inserts can bechanged in a 20 to 30 minute period rather than the 4 to 6 hoursrequired with prior art devices. Thus end users have advantages gainedby the use of reduced tooling cost, as only inserts rather than entiremolds need be made for different products, and reduced change over time.

1. An injection mold comprising: a cavity plate fixed along an axis, anda core plate moveable along said axis; the moveable core plate and thefixed cavity plate each having the same number of cavities; the moveablecore plate being mounted on an axle positioned along the axis, and drivemeans being provided to rotate the axle and thereby to rotate themoveable core plate; the drive means comprising a pinion on said axle,and at least one moveable rack engaged with said pinion; one or moreinsert slots in the cavity plate and the core plate; each insert slotbeing capable of receiving an insert; the cavity plate and the coreplate having guide means thereon; a plurality of inserts; the insertshaving complementary guiding means thereon to enable a selected insertto be entered into and subsequently removed from a cavity by engagementof the guide means with the complementary guiding means; the guide meansbeing constructed and arranged so that, in use, an insert may be engagedwith the guide means and moved along the guide means to the insert slot;and wherein each cavity plate is able to receive at least two inserts.2. The injection mold according to claim 1, wherein the guide meanscomprise a channel or channels, or rib or ribs.
 3. The injection moldaccording to claim 1, wherein each guide means comprises a pair ofspaced apart mutually inwardly facing channels extending in a directionparallel to a line transverse to an axis formed by the movement of moldparts to open and close the mold in use.
 4. The injection mold accordingto claim 3, wherein the cavity plate includes a removable member, whichwhen engaged with the remainder of the cavity plate closes the channelsto substantially prevent movement of an insert into or out of the insertslot.
 5. The injection mold according to claim 3, wherein the core plateincludes a removable member, which when engaged with the remainder ofthe core plate, closes the channels to substantially prevent movement ofan insert into or out of the insert slots.
 6. The injection moldaccording to claim 1, wherein the complementary guiding means comprise apair of ribs able to engage a channel in the cavity plate.
 7. Theinjection mold according to claim 1, wherein the moveable core plate hasat least two cavities and is rotatable about the axis to present aselected cavity to each cavity in the fixed cavity plate.
 8. Theinjection mold according to claim 1, further comprising a pair ofparallel racks; the pinion being positioned between and engaging eachrack.
 9. The injection mold according to claim 8, wherein the racks areoperated by a piston and cylinder device.
 10. An injection moldaccording to claim 9, wherein each rack is moved by a piston andcylinder assembly arranged to rotate the pinion in an oppositedirection.